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The voltage rating of a parallel plate capacitor is 500 V. Its dielectric can withstand a maximum electric field of 10⁶ V m⁻¹. The plate area is 10⁻⁴ m². What is the dielectric constant if the capacitance is 15 pF? (Takeε₀=8.86×10⁻¹² C² N⁻¹ m⁻²)

Asked in JEE Main 8th April 1st Shift 2019 · Capacitance of a conductor and a capacitor

Answer: (2) 8.5

Step-by-step solution

The capacitor is used right up to its rating, so the maximum field appears across the plates: d=V/(Eₘₐₓ)=(500)/(10⁶)=5×10⁻⁴ m.

Without the dielectric, C₀=(ε₀A)/d=(8.86×10⁻¹²×10⁻⁴)/(5×10⁻⁴)=1.772×10⁻¹² F=1.772 pF.

C=KC₀⇒ K=(15)/(1.772)=8.47.

So K≈8.5.

Why the other options are wrong

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